Petroleo Brasileiro, or Petrobras, Brazilâs state-owned oil company, on Thursday said well tests revealed its Tupi field may contain as much as 8bn barrels of oil and natural gas, which would considerably bolster the countryâs energy clout.

The estimate, if correct, would raise the countryâs reserves by 62 per cent and just about put Tupi on par with Norwayâs 8.5bn barrels of proved oil reserves.

Oct-24Brazil has 14.4bn barrels of proved reserves of oil and natural-gas equivalent.

The news pushed up Petrobrasâ shares 9.95 reais, or 14.2 per cent, to 80.2 on the SÃ£o Paulo stock exchange, the biggest rise in more than nine years.

It also lifted the shares of its partners â BG group of the UK, which holds a 25 per cent stake, and Galp Energia of Portugal, which holds 10 per cent. BG Groupâs shares rose 9.8 per cent to 989p in London and Galp Energia reported its biggest one-day gain in Lisbon, rising 14 per cent to a record close of â¬12.35.

Petrobrasâ news release contained few details beyond the fact that the estimates were made after analysis of the formation tests for a second well in the area.

The company also said the oil within was light, which is more valuable because it is cheaper to refine than the heavier crude oil that Brazil mostly produces.

âTupi changes everything for Brazil and Petrobras,ââ said Carlos Renato Nunes, an oil analyst with SÃ£o Paulo-based brokerage Coinvalores CCVM who has a buy recommendation on Petrobras shares.

âTupi is not only huge, its light oil offers huge cost advantages.ââ

And at a time when oil is heading towards $100 a barrel, and energy security is high on the agenda of many governments, the news is sure to boost Brazilâs economic influence. Petrobras, already a well-respected national oil company on the world stage, is likely to receive a further boost from the discovery.

âBrazil needs time to evaluate its new oil potential,ââ Dilma Rousseff, president Luiz Inacio Lula da Silvaâs cabinet chief, said at a news conference in Rio de Janeiro.

âThis could make Brazil jump from an intermediate producer to among the worldâs largest producers.ââ

Tupi is three-quarters the size of Kazakh_stanâs Kashagan field, which holds 12bn barrels of recoverable crude and was the biggest find in the past 30 years.

There have only been a few gas discoveries in the past 20 years that would rival it, including the Shtokman field in Russia at 23bn barrels of oil equivalent, and two other Russian finds in the 5bn to 10bn range, Andy Latham, vice-president of exploration services at Wood Mackenzie Consultants in London, said.